816
FXUS63 KDMX 241714
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1214 PM CDT Sun Aug 24 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Cool and dry over the next several days.

- Little to no precipitation this week.

&&

.UPDATE...
Issued at 331 AM CDT Sun Aug 24 2025

No significant changes to the going forecast. Remaining mostly
dry and cool over the next several days as the northwest flow
persists aloft and Canadian high pressure ridging at the
surface. The wind will become diurnally breezy again today with
some gusts in the 20 to 25 mph range. Cumulus develop will occur
again today as well and there will be a bit more vertical extent
to tops than Saturday. Still not expecting enough cloud depth
for sprinkles/light rain with it capped by an inversion aloft.

&&

.DISCUSSION...
Issued at 145 PM CDT Sat Aug 23 2025

At 500 MB a large cyclone is located over Ontario this
afternoon, with a deep-layer ridge over the southwestern U.S.
around the Four Corners region. Between these systems
northwesterly steering flow is in place over Iowa, pushing the
frontal boundary that crossed our service area last night
farther south into Missouri. Notably cooler and drier area is
flowing into the area, bringing an end to a relatively long
period of warm and humid weather that had worn out its welcome.
While dewpoints have been in the 70s for most of the last month,
the current dewpoints are now in the low to mid-50s in most of
our area making it much more comfortable outside. This overall
weather pattern will hold for several days, at least through
Tuesday, with a series of shortwave impulses rounding the base
of the 500 MB cyclone over Minnesota, Wisconsin, and Iowa during
that time. The first of these is crossing the region today,
combining with diurnal warming to generate a field of
stratocumulus clouds covering most of MN and WI and spreading
into northern and northeastern Iowa. Some short-range model
solutions are popping sprinkles within this cloud field, mainly
just to our northeast, but most remain dry and the probability
of rain in our forecast area is very low, thus no mention is
carried in the ongoing forecast.

There is also some question as to whether sprinkles will occur
during the day on Sunday, somewhat analogous to today except
that on Sunday the shortwave moving overhead is deeper.
A few CAMs pop tiny spots of rain but others do not, and
although forecast soundings do indicate a shallow cloud layer
with some instability (25-50 J/kg) in it, there will be about 5
KM of very dry air between there and the surface. The most
likely scenario is that shallow cloud cover is somewhat more
expansive than indicated by consensus model guidance, but any
precipitation that is produced likely does not reach the
surface or if it does would be only isolated spits of rain.
Have thus left any mention out of the Sunday forecast for now.

With several days of cool and dry weather on tap through about
Tuesday, after the preceding multiple weeks of hot and humid
weather, blended model temperature guidance is really an average
of two very different camps. Raw model output is clustered in a
range several degrees lower than a warmer cluster of bias
corrected output. This is typical of the days after a notable
weather regime change, and it is likely that the raw output
range is the more reasonable and accurate prediction. Therefore,
have continued the trend of nudging our official forecast down
into that range, a little lower than the overall guidance mean
values. The coolest readings should come Monday into Tuesday as
a surface high settles over Iowa, with morning lows in the mid
to upper 40s each day and daily highs only in the upper 60s to
lower 70s.

By Tuesday night/Wednesday we will see a synoptic pattern
change, as the southwestern U.S. ridge flattens out and the
eastern Canada low moves off to the northeast. This will result
in a weaker steering flow regime over the Midwest, and rapidly
decreasing predictability in forecast details. Overall it should
keep things relatively quiet in Iowa, with only slowly
moderating temperatures and no strong storm systems foreseen
during the coming week, however rain chances may return at times
during the latter half of the week. Nevertheless, it is hard to
see a return of the summer weather we endured for the last
several weeks, and it appears we have now entered the long slide
toward early autumn.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1213 PM CDT Sun Aug 24 2025

VFR conditions are anticipated through the TAF period, with no
aviation weather concerns.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

UPDATE...Donavon
DISCUSSION...Lee
AVIATION...Lee